Linköping University Medical Dissertations No. 1036
Dynamic knee stability
after
anterior cruciate ligament
injury
Emphasis on rehabilitation
Sofi Tagesson
Division of Physiotherapy Department of Medical and Health Sciences Linköping University, Sweden
© Sofi Tagesson, 2008 sofi.tagesson@ihs.liu.se http://www.imh.liu.se Electronic publication of the thesis: http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva‐10498 Published articles have been reprinted with the permission of the copyright holder. Paper I reprinted with permission of the Scandinavian Journal of Medicine & Science in Sports, Blackwell Publishing. Paper II reprinted with permission of the Journal of Strength and Conditioning Research, Allen Press Publishing Services.
Paper III reprinted with permission of the American Journal of Sports Medicine, Sage Publications, Inc. Printed in Sweden by LiU‐Tryck, Linköping, Sweden, 2008 ISBN 978‐91‐85895‐05‐2 ISSN 0345‐0082
To my family
Contents
CONTENTS
ABSTRACT ... 1 LIST OF PAPERS ... 3 DESCRIPTION OF CONTRIBUTION... 4 ABBREVIATIONS... 5 DEFINITIONS... 6 INTRODUCTION... 8 Anatomy and function of the knee joint... 8 Mechanical properties of ligaments... 8 Anterior cruciate ligament ... 9 ACL injury... 10 Incidence and injury mechanisms... 10 Consequences of the injury ... 11 Static knee stability ... 12 Dynamic knee stability... 12 Proprioception and neuromuscular control ... 13 Muscle function... 14 Treatment of ACL injury... 15Contents Rationale for the thesis ... 23 AIMS OF THE THESIS... 24 General aim... 24 Specific aims ... 24 MATERIALS AND METHODS... 26 Design ... 26 Overview of the studies... 26 Subjects... 27 Study I and II... 28 Study III... 28 Study IV ... 29 Equipment... 29 Electrogoniometer ... 29 Electromyography ... 31 Isokinetic device... 32 Force measurements... 32 Questionnaires about subjective knee function and activity level... 33 Assessments ... 35 Static tibial translation (study I, III, IV) ... 35 Dynamic tibial translation and electromyography (study I, III, IV) ... 35 Muscle strength (study II, III, IV)... 38 Functional performance (study III)... 40 Knee joint circumference (study III, IV) ... 40 Passive range of motion (study III, IV)... 41 Data analysis... 41 Tibial translation ... 41 Electromyography ... 42 Muscle strength... 42 Statistical analyses... 42 Ethical considerations ... 44 RESULTS ... 45
Contents Tibial translation and muscle activation after an exercise session in uninjured individuals (study I) ... 45 Static tibial translation ... 45 Dynamic tibial translation... 45 Electromyography ... 46 The procedure for the establishment of one repetition maximum (study II) ... 47 Reliability of squat on one leg (study II) ... 47 Reliability of seated knee extension on one leg (study II)... 47 Effects of rehabilitation programs with quadriceps strengthening in closed or open kinetic chain in patients with ACL deficiency (study III) 49 Static tibial translation ... 49 Dynamic tibial translation... 49 Electromyography ... 50 Muscle strength... 51 Functional performance... 51 Swelling and passive range of motion ... 52 Follow‐up two to three years after the injury... 52 Tibial translation and muscle activation during rehabilitation exercises five weeks after ACL reconstruction (study IV)... 53 Static tibial translation ... 53 Dynamic tibial translation... 53 Electromyography ... 53 The ACL reconstructed leg compared to the uninjured leg (study IV) .... 55 Static tibial translation ... 55 Dynamic tibial translation... 55 Electromyography ... 55 The ACL reconstructed leg compared to the ACL deficient leg (study IV)56
Contents Main findings ... 58 Dynamic knee stability during and after exercises in closed and open kinetic chain... 59 Altered dynamic stability ... 61 Muscle activation during and after exercises in closed and open kinetic chain... 64 Muscle function after rehabilitation... 66 Strength training and dosage of rehabilitation programs ... 68 Non‐surgical treatment or ACL reconstruction ... 69 Methodological considerations... 70 Tibial translation ... 70 Electromyography ... 72 Measurements of muscle strength and functional performance... 74 Measurements on uninjured individuals and patients with ACL injury75 Selection of leg for assessment... 76 Using the uninvolved leg as a reference ... 76 Design of the randomised clinical study (III)... 77 Compliance to the rehabilitation programs... 77 Contribution to research... 78 Clinical implications ... 78 Future research ... 79 CONCLUSIONS ... 80 SAMMANFATTNING ... 82 ACKNOWLEDGEMENTS ... 84 REFERENCES ... 86
Abstract
ABSTRACT
Anterior cruciate ligament injury leads to increased sagittal tibial translation, and perceptions of instability and low confidence in the knee joint are common. Many patients have remaining problems despite treatment and are forced to lower their activity level and prematurely end their career in sports. The effect of ACL reconstruction and/or rehabilitation on dynamic knee stability is not completely understood. The overall aim of this thesis was to study the dynamic knee stability during and after rehabilitation in individuals with ACL injury. More specific aims were 1) to elaborate an evaluation method for muscle strength, 2) to evaluate the effect of exercises in closed and open kinetic chain, and 3) to evaluate dynamic knee stability in patients with ACL deficiency or ACL reconstruction.
Sagittal tibial translation and knee flexion angle were measured using the CA‐4000 computerised goniometer linkage. Muscle activation was registered with electromyography.
The intra‐ and inter‐rater reliability of 1 repetition maximum (RM) of seated knee extension was clinically acceptable. The inter‐rater reliability of 1RM of squat was also acceptable, but the intra‐rater reliability was lower. The systematic procedure for the establishment of 1RM that was developed can be recommended for use in the clinic.
One specific exercise session including cycling and a maximum number of knee extensions and heel raises did not influence static or dynamic sagittal tibial translation in uninjured individuals. A comprehensive rehabilitation program with isolated quadriceps training in OKC led to significantly greater isokinetic quadriceps strength compared to CKC rehabilitation in patients with ACL deficiency. Hamstring strength, static and dynamic translation, and functional outcome were similar between groups. Five weeks after ACL reconstruction, seated knee extension produced more anterior tibial
Abstract
knee extension angle during gait and increased hamstring activation during activity, which reduces the dynamic tibial translation. Patients with ACL deficiency that completed a four months rehabilitation program used a movement pattern that was more close to normal.
List of papers
LIST OF PAPERS
This thesis is based on the following papers, which are referred to in the text by their Roman numerals:
I. Sofi Tagesson, Birgitta Öberg, Joanna Kvist. Passive and dynamic
translation in the knee is not influenced by knee exercises in healthy individuals. Scandinavian Journal of Medicine & Science in Sports 2005; 15 (3) 139‐147.
II. Sofi Tagesson, Joanna Kvist. Intra‐ and interrater reliability of the
establishment of one repetition maximum on squat and seated knee extension. Journal of Strength and Conditioning Research 2007; 21 (3) 801‐ 807.
III. Sofi Tagesson, Birgitta Öberg, Lars Good, Joanna Kvist. A
comprehensive rehabilitation program with quadriceps strengthening in closed versus open kinetic chain in patients with anterior cruciate ligament deficiency: a randomized clinical trial evaluating dynamic tibial translation and muscle function. American Journal of Sports Medicine 2008; 36 (2) 298‐307.
IV. Sofi Tagesson, Birgitta Öberg, Joanna Kvist. Tibial translation and
muscle activation during rehabilitation exercises 5 weeks after anterior cruciate ligament reconstruction. Submitted 2007.
Decription of contribution
DESCRIPTION OF CONTRIBUTION
Paper I Study design Joanna Kvist, Sofi Tagesson, Jan Gillquist Data collection Sofi Tagesson Data reduction Sofi Tagesson Data analysis Sofi Tagesson, Joanna Kvist, Birgitta Öberg Manuscript writing Sofi Tagesson Manuskript revision Joanna Kvist, Birgitta Öberg Paper II Study design Sofi Tagesson, Joanna KvistData collection Sofi Tagesson, Per Axelsson, Bettina Hillborg, Marie Rydén Data reduction Sofi Tagesson Data analysis Sofi Tagesson Manuscript writing Sofi Tagesson Manuscript revision Joanna Kvist, Birgitta Öberg Paper III Study design Sofi Tagesson, Joanna Kvist, Birgitta Öberg, Lars Good Data collection Sofi Tagesson Data reduction Sofi Tagesson Data analysis Sofi Tagesson Manuscript writing Sofi Tagesson Manuscript revision Joanna Kvist, Birgitta Öberg, Lars Good Paper IV Study design Sofi Tagesson, Joanna Kvist, Birgitta Öberg Data collection Sofi Tagesson Data reduction Sofi Tagesson Data analysis Sofi Tagesson Manuscript writing Sofi Tagesson Manuscript revision Joanna Kvist, Birgitta Öberg
Abbreviations
ABBREVIATIONS
ACL Anterior cruciate ligament CKC Closed kinetic chain EMG Electromyography ICC Intra class correlation coefficient KOOS Knee injury and Osteoarthritis Outcome Score M Mean MIVC Maximal isometric voluntary contraction OKC Open kinetic chain RCT Randomised Controlled Trial RM Repetition maximum ROM Range of motion SD Standard Deviation VAS Visual Analogue ScaleDefinitions
DEFINITIONS
ACL deficiency The state or condition of lacking a substance, quality, or characteristic essential for completeness;234 i.e., absence of the anterior cruciate ligament
ACL graft The biological substitute used for reconstruction of a ruptured anterior cruciate ligament
Closed kinetic chain exercise
Exercise that is modelled as a closed linkage where a movement in one joint simultaneously produces movements in other joints of the extremity243, 339 Compliance A patient’s collaboration with treatment directions Concentric muscle action When a muscle shortens while producing force155 Dynamic knee stability
The ability of the knee joint to remain stable during physical activity.342 Synonymous with functional stability Dynamic tibial translation Anterior tibial translation during activity Eccentric muscle action When a muscle lengthens while producing force155
Giving way The knee buckles or it feels as if it would not hold the patient’s weight47
Instability A condition of a joint characterized by an abnormal increased range of motion due to injury to the ligaments, capsule, menisci, cartilage or bone234
Laxity Slackness or lack of tension (a characteristic of a ligament) and looseness, referring to a normal or abnormal range of motion of a joint234
Definitions
Muscle strength The maximal force a muscle or muscle group can generate at a specified velocity155
Neuromuscular control
The ability to produce controlled movement through coordinated muscle activity342
Open kinetic chain exercise
Exercises that isolate one link of the kinetic chain and where the distal segment is free to move243, 339
Reliability Consistency of measurements and the absence of random and systematic measurement error12, 313
Repetition maximum
The heaviest resistance that can be lifted for one complete repetition of an exercise76, 155
Static tibial translation
Total sagittal tibial translation during the Lachman test
Strain Change in the dimension of a material divided by its original size176
Tibial position Relative location of tibia with respect to femur
Torque Moment of force (term generally applied to rotation of shaft) (unit Nm)176
Translation A type of motion or displacement of a rigid body in which all lines attached to it remain parallel to their original orientation176, 234
Introduction
INTRODUCTION
Anatomy and function of the knee joint
The knee joint has six degrees of freedom, three rotational and three translational.103 It is a complex joint that provides both stability, to allow weight bearing, and mobility. The knee joint obtains just modest stability from the bones due to incongruity of the tibia and femoral condyles. The menisci, on the other hand, provide stability through improved joint congruity because of their shape, orientation, and functional properties.295 In addition, the ligaments, capsule, and the muscolutendinous soft tissue that surrounds the knee interact with complex gliding and rolling movements in the joint to maintain functional stability.342 The knee ligaments guide the skeletal segments during motion and are the primary restraints to knee joint translations during passive loads.20
There is great range of movement (ROM) in flexion and extension in the sagittal plane, and a small amount of rotation in the transversal plane, especially when the knee is flexed and the foot is not fixed to a surface. Movements in the knee joint are a combination of rolling and gliding. Beginning with full extension in a weight bearing position, the femoral condyles only roll, and with increased flexion the sliding movement becomes increasingly more significant. At the end of flexion, the condyles only slide.103, 242 The tibial plateaus slopes approximately 9° posterior.103, 204, 229 During weight‐bearing, a vertical compression causes the tibia to translate anteriorly.67, 170, 295, 326 At activities such as running and cutting the knee is flexed, which means that the tibial plateau is almost parallel with the weight‐ bearing surface.69
Mechanical properties of ligaments
Ligaments are viscoelastic structures and have a combination of elastic and viscous qualities. An elastic material returns to its original shape after it has
Introduction
been exposed to load. A viscous material does not deform initially when loaded; the strain is delayed. Moreover, when a deformation has taken place, the material does not recover. A viscoelastic material deforms slowly in a nonlinear manner. Also, it slowly and nonlinearly returns to its original size and shape after the load has been removed. The mechanical properties of ligaments can be displayed in a load‐deformation curve, called a stress‐strain curve (Figure 1). Stress is defined as the internal force per unit area. Strain is defined as the percentage elongation over the original length.176 The beginning of the stress‐strain curve has a linear relationship and corresponds to the elasticity of the ligament. The elastic limit (Figure 1) indicates the point where the ligament will not return to its original length, i.e., plastic deformation. With increased strain, a progressive rupture of the material occurs, and the rupture point (Figure 1) is the point when a total ligament rupture occurs. When a ligament is loaded and unloaded repeatedly, the cycles will not follow the same path. The area between the loading and unloading curves corresponds to internal energy loss. This phenomenon is called hysteresis.176 Figure 1 Stress‐strain curve that displays the mechanical properties of ligaments.
Anterior cruciate ligament
Stress Strain Elastic limit Rupture point Elastic range Plastic rangeIntroduction
restraint to anterior tibial translation, and it provides an average of 86% of the total resisting force. Additionally, it is a secondary restraint to rotation, especially internal rotation of tibia.45 Accordingly, the strain in the ACL is increased when the tibia is exposed to anterior force. After 15 to 25% of elongation of the ACL, in relation to its original length, plastic deformation occurs.173 The average strain in the anteromedial bundle of the ACL during 90N Lachman test is 2.16 ± 1.1% and during 150N it is 3.4 ± 1.8%.82 The failure load of an ACL is reported to be about 2160 ± 157N in young individuals, and ultimate load and energy absorbed decrease significantly with age.347, 348 Another study states that load at failure is about 1818 ± 699N in males and about 1266 ± 527N in females.52 Moreover, the strain at failure was 30 ± 6% in males and 27 ± 8% in females.52 During daily activities and commonly prescribed rehabilitation exercises, the ACL is loaded only to about 20% of its failure capacity.31, 32, 124
ACL injury
Incidence and injury mechanisms
Anterior cruciate ligament injury is the most common total ligament rupture in the knee.34, 208 The injury is relatively uncommon in the general population; the yearly incidence is 0.3 to 0.81 per 1000 inhabitants.90, 227 The incidence is considerably greater among athletes.104 An estimated 80000 ACL injuries occur annually in the United States.104 In Sweden, about 6000 ACL injuries occur yearly, and approximately 3000 ACL reconstructions are performed.1 Soccer is the most common activity that results in injury,90 and ACL injuries represent 43% of all soccer related injuries.275 Also basketball, handball, football, alpine skiing and gymnastics are common activities that result in injury.41, 127, 205, 220, 221, 256 Rates of ACL injury in women’s soccer and basketball have been reported to be 0.32 and 0.28 injuries per 1000 athlete exposures respectively. Correspondingly, rates of ACL injury for men are 0.11 and 0.08 injuries per 1000 athlete exposures respectively.205
More males than females sustain an ACL injury due to the greater absolute number of male participants in sport activities.104 However, the risk of sustaining an ACL injury is reported to be two to eight times higher among
Introduction
female athletes compared to their male counterpart. 4, 8‐10, 104, 117, 139, 221, 275 The females also get injured at a younger age than men.275 A recent study found small gender differences in the overall risk of sustaining an ACL tear although gender differences in injury rates were found when specific sports were compared.218
Anterior cruciate ligament injuries are thought to occur due to unsuccessful postural adjustments and abnormal dynamic loading, i.e., inter‐segmental loads in the knee joint.105 The majority of the ACL injuries (about 70%) occur in a non‐contact situation.41, 104 Non‐contact injuries often occur with the knee close to extension during a sudden deceleration or landing motion. Contact injuries are frequently the result a contact blow to the lateral aspect of the leg or knee, a motion that causes a valgus collapse.41 The injury mechanism for ACL injuries in female team handball is reported to be a forceful valgus collapse with the knee close to full extension combined with external or internal tibial rotation.238 Associated injuries in the capsule, ligament or menisci are common, and most patients have complex injuries.90, 154, 239
Consequences of the injury
An ACL rupture leads to increased laxity in the knee.45, 63, 154, 184, 232, 284 In the ACL deficient knee, anterior tibial translation is limited by secondary restraining structures, such as the posterior joint capsule, the collateral ligaments, and the menisci.45, 201 The injury leads to loss of mechanoreceptor feedback and loss of reflex muscular contractions.19‐21, 25, 26, 144, 145, 162, 305 Furthermore, the ACL injury often results in perceptions of instability in the knee joint.47, 236 Giving way is common, and this is described as the knee buckles or a feeling as if the knee would not hold the patient’s weight.47 The patients frequently describe low confidence in their knee joint. Individuals are often forced to lower their activity level and prematurely end their career in sports.96, 163, 169, 236, 275, 303
Introduction
50 years with early‐onset osteoarthritis.185 The joint instability280 and muscle weakness115 are thought to lead to progressive arthritic changes. Some patients use a stabilization strategy after the injury that stiffens the knee joint, and that may lead to changed loading on the joint surfaces and excessive joint contact forces. This could damage articular structures.279 Moreover, intra‐articular pathogenic processes are initiated at time of the injury, and this together with the changed loading pattern on the joint surfaces is thought to contribute to the osteoarthritis.185, 283 In addition, associated injuries, especially menisci injury, probably increase the risk of future osteoarthritis.5, 95, 147, 185 An ACL reconstruction does not seem to prevent osteoarthritis.60, 185
Static knee stability
The knee anatomy includes a supportive system of osseous, contractile, and non‐contractile structures, which together contributes to stability in the joint.103 In a passive situation, for example during a static laxity test, the bones and other non‐contractile structures provide joint stability. An ACL injury leads to decreased static stability due to loss of an important stabilizer.45, 154, 232 The static tibial translation is frequently assessed when evaluating treatment after ACL injury.46, 206, 249, 287 However, static tibial translation does not correlate with functional outcome in patients with ACL deficiency71, 134, 246, 301 or ACL reconstruction121, 287 or with quadriceps or hamstring muscle strength in patients with ACL deficiency.246 Furthermore, the static tibial translation does not correlate with the dynamic tibial translation, i.e. translation during activity.166
Dynamic knee stability
Dynamic knee stability is the ability of the knee joint to remain stable when it is exposed to the rapidly changing loads that occur during activity.342 Dynamic stability depends on integration of articular geometry, soft tissue restraints, and the loads applied to the joint through weight bearing and muscle activation.342 Generally, several ligaments work synergistically to provide joint stability.103 In addition, joint compressive forces, gained by weight bearing and muscle activity,188, 195, 196 provide additional stability.132 The neuromuscular system regulates joint motion.122, 137, 293, 342 When high loads are placed on the
Introduction
ligaments and other soft tissues, for example during some high speed sport activities, additional stabilizing forces are required to keep the strain in knee ligaments within safe ranges. Although muscle contraction can stabilize a mechanically unstable knee, these contractions can increase joint stiffness. Co‐ contraction of agonist‐antagonist may further enhance joint stiffness by increasing the joint compression.179, 180, 188, 326, 342 Increased joint stability, and accordingly a probable reduction in ACL strain, can be the result of co‐ contraction.18, 180, 260, 305 Co‐contraction regulates joint motion, and the antagonist can regulate the effect of gravity and velocity of a movement. When performing an unpractised exercise, increased co‐contraction is present. However, as a skill is acquired by practice, the activation of the antagonist muscle is reduced, and the efficiency of the movement is increased.305 In an ACL injured knee, the muscles play an even greater role in achieving dynamic stability. Some patients can maintain knee stability in dynamic situations despite a mechanically unstable knee.301 Dynamic tibial translation is a factor of importance for good function after ACL injury.165 It has been described that patients with ACL deficiency who do not function well after the injury, non‐ copers, use a joint stiffening strategy with increased co‐contraction. In contrast, patients who function well after the injury, copers, use a movement pattern that is more close to normal.278‐280
Proprioception and neuromuscular control
The sensorimotor system represents complex neurosensory and neuromuscular processes.178 Proprioception is the afferent information arising from internal peripheral areas of the body that contribute to postural control, joint stability, and several conscious sensations.264 Proprioception involves acquisition of stimuli from mechanoreceptors primarily situated in the muscle, tendon, ligament, and capsule. The mechanoreceptors sensitive to this stimuli are Ruffini receptors, Pacinian corpuscles, Golgi tendon organ like endings, and free nerve endings. Sensory input is integrated into the central nervous
Introduction
the ligament transmit impulses through the nervous system to the muscles. When a ligament is overstretched, strong impulses are forwarded to muscles that are synergists to the ligament. A subsequent muscle contraction may protect the ligament from getting injured.20, 162 However, the cruciate ligament reflex has a latency that is too long to activate the muscles in time to prevent ligament rupture in sport accidents.162, 305
There are mechanoreceptors situated in the ACL.144, 145, 285, 286, 305 The ACL has a proprioceptive role, and loss of proprioceptive feedback in the ACL injured knee may be of importance in functional knee instability.19‐21, 25, 26, 144, 145, 162, 305 Reflex hamstring contraction as a response to shear force on tibia or stress of the ACL have been reported.25, 91, 304 ACL deficient knees have longer latency of the reflex hamstring contraction compared to uninjured knees, and this is suggested to be a factor contributing to functional instability in the injured knee joint.25, 26, 162, 305 Thus normal knee function depends on intact neuromuscular control. The results regarding if afferent input and the reflex muscle contraction are restored through an ACL reconstruction are somewhat contradictory, although deficits seems to persist to some degree.19, 144, 162, 259
Muscle function
Muscle function depends on neural, muscular, and biomechanical factors.75 Weakness of the thigh muscles, especially the quadriceps, is a common consequence after knee trauma. Joint pathology can cause inhibition of muscle activity.135, 136, 213, 312 Moreover, immobilization results in decreased muscle volume and function. Even after one or two weeks of immobilization the muscle is adversely affected.138, 146 Restoration of muscle function and strength is a central goal in ACL rehabilitation, since good muscle strength has been shown to be important after ACL injury or reconstruction. The rehabilitation needs to include all lower extremity muscles, although quadriceps weakness is one of the major challenges.268 Many patients have muscle weakness in spite of completed rehabilitation after ACL injury or reconstruction,16, 71, 74, 119, 149, 187, 241, 246, 267, 317, 341 and quadriceps weakness is common in patients who do not compensate well for the injury.71 Moreover, quadriceps atrophy or weakness have been noted to be correlated to poor knee function.71, 98, 143, 152, 216, 230, 300, 338, 343
It is unclear why quadriceps muscles weaken. Activation failure and lack of control of the quadriceps muscle have been reported,54, 135, 136, 187, 330, 331 and that
Introduction
can be caused by abnormal articular afferent information and reflex inhibition in the muscle.78, 135, 136, 157, 158, 213, 299, 312 Swelling has an inhibitory effect on the quadriceps muscle.78, 128, 153, 213, 325 It is also known that pain may affect the ability to activate the muscle.56, 213, 311, 333 In addition, instability can lead to a different movement pattern, which probably alters the muscle recruitment.279 A reduced external flexion moment has been found in patients with ACL deficiency.30, 278 This is interpreted as a quadriceps avoidance pattern and is suggested to be an adaptive strategy to decrease the anterior directed force on the tibia.30 However, the occurrence of this gait alteration is questioned.270 Furthermore, weakness in thigh muscles, particularly the quadriceps, persists with lack of structured rehabilitation,328 and it is questionable if the strength training previously performed has been sufficient.206, 277
Treatment of ACL injury
The treatment choices for individuals with ACL injury are either surgery and subsequent rehabilitation or exclusively rehabilitation. The surgery involves a reconstruction of the ligament with a graft. Candidates for surgery are young active individuals, patients with persistent functional instability and giving way symptoms after the rehabilitation, and combined ligamentous and meniscal injuries.60, 68, 87, 274 Approximately one‐third of the patients with an ACL injury compensate enough to resume activity. One‐third can partly compensate but are forced to give up many activities. One‐third experience instability despite rehabilitation and are referred to surgical intervention.235 Irrespective of the possible reconstruction, the rehabilitation exerts great influence on the healing response,35 and structured rehabilitation significantly helps patients gain dynamic stability in the knee joint.35, 51, 70, 87
Introduction
and quadriceps weakness have resulted in the use of the hamstring graft, a technique that has become more common.86, 88, 350 Earlier meta‐analyses comparing patellar tendon and hamstring tendon graft concluded that patellar tendon grafts had a lower rate of graft failure88 and resulted in better static knee stability88, 357 and increased patient satisfaction88 compared to hamstring tendon graft. However, a recent meta‐analysis revealed that the knee stability and graft failure with the two graft alternatives are similar.38 In addition, use of the hamstring tendon graft resulted in a lower rate of anterior knee pain38, 88 and extension deficits38 compared to patellar tendon graft. There were no differences between the graft alternatives with respect to returning to previous sporting activities.88
An ACL reconstruction can reduce the static knee laxity to within normal or clinically satisfactory limits.34, 43, 244, 284, 318, 356 However, the procedure does not seem to restore normal tibiofemoral kinematics.27, 34, 43, 183, 235, 244, 318, 356 Another study reported that ACL reconstruction with hamstring graft restored the tibiofemoral contact pattern to that of the uninjured contralateral knee. However, the kinematics of both knees appears to change with time.284 Yet, an ACL reconstruction may decrease the risk of future meniscal or cartilage injury requiring surgery.68 However, the risk of osteoarthritis does not seem to be reduced.60, 185
Rehabilitation after ACL injury or reconstruction
The rehabilitation of patients with ACL deficiency aims to improve the dynamic stability despite the decreased mechanical stability. The main goal of the rehabilitation after ACL rupture or reconstruction is to restore knee function by enhanced neuromuscular control, which can be achieved by training of muscle strength, coordination, and proprioceptive ability.53, 269, 342 Neuromuscular training programs for patients with ACL reconstruction aim to improve muscle activation, increase dynamic joint stability, and relearn movement patterns and skills used during daily activities and sports activities.269 A neuromuscular training program is reported to be effective in improving the knee function.266 Many other rehabilitation programs also include exercises to improve the neuromuscular function.
Current practices commonly employ accelerated rehabilitation, permitting immediate full weight bearing and restoration of full range of motion after
Introduction
ACL reconstruction.288, 291, 329 The rehabilitation program needs to be progressed according to guidelines.6 Progression to the next phase is usually allowed after fulfilment of certain criteria.51, 53, 219 There is, however, no consensus regarding the optimal rehabilitation regimen following ACL deficiency or reconstruction.33, 35, 292, 327
After a ligament injury or surgery the injury site should be protected during the first healing phases so the tissue can regain a certain amount of strength. Rehabilitation after ACL reconstruction needs to avoid great anterior tibial translation to protect the graft from excessive strain and pathological elongation.33, 35 In addition, patients with ACL deficiency should probably avoid large anterior tibial translation in the first rehabilitation phase to avoid excessive strain on secondary stabilizers. The secondary restraining structures are placed under increased tension as the load‐bearing capacity of the ACL has been decreased or abolished due to the injury, a situation that may cause further loosening of the joint.45 In the later phase of healing, it is however, known that application of some amount of stress on the healing tissue will improve healing and contribute to increased stiffness and improved mechanical properties and remodelling of the ligament or graft.308, 324, 349 Consequently, some strain during the healing process increases graft strength, whereas excessive strain can stretch or rupture the graft. When designing a rehabilitation program for patients after ACL reconstruction it is fundamental to restore lower extremity function and at the same time optimally load the ACL graft.268 It is, however, unclear how much strain can be accepted during different healing phases after an ACL reconstruction.
Closed and open kinetic chain
Rehabilitation exercises can be classified into closed kinetic chain (CKC) or open kinetic chain (OKC) exercises. Exercises in CKC are modelled as closed linkages where a movement in one joint simultaneously produces movements in other joints of the extremity. Exercises in OKC isolate one link of the kinetic
Introduction
on the tibia relative to femur,31, 46, 77, 84, 171, 190, 337, 354 increased tibiofemoral compressive forces,46, 77, 84, 337 and increased hamstrings co‐contraction.31, 171 In addition, CKC exercises are similar to functional activities.77, 126 A CKC exercise involves motion in all joints in the extremity, which requires coordinated muscle activity in several muscles to control all segments in the extremity.66, 140 Moreover, there are fewer reported patellofemoral complications related to CKC exercises than to OKC exercises.46, 77, 126 However, there is evidence that CKC and OKC exercises are equally effective in rehabilitation for patellofemoral pain syndrome.112
Quadriceps contraction to near full extension leads to strain on the ACL. Knee extension exercises involve different strain values depending on knee flexion angle and the magnitude of muscle contraction. In contrast, exercises that involve isolated hamstring contraction do not strain the ACL at any knee position or magnitude of the muscle contraction.11, 32, 35, 36, 107, 197, 260, 337 Furthermore, exercises in CKC cause smaller anterior tibial translation than exercises in OKC in patients with ACL deficiency.171, 354 The smaller translation can be explained by higher joint compression forces that decrease anterior‐ posterior translation during a CKC exercise.326, 337 However, application of a compressive load and muscle activation produces an anterior shift of the tibia326 that could strain the ACL, a result that supports the fact that weight bearing also increases ACL strain.84 In addition, it is unclear whether small differences in tibial translation would produce excessive increase in the strain on the ACL or secondary restraints.131 Moreover, recent research has proposed that the effect of CKC and OKC exercises do not differ in terms of graft healing, postoperative knee function, and patient satisfaction.83 There is still lack of evidence concerning what is optimal rehabilitation for ACL injured patients. Evidence regarding the strain on the ACL during various types of exercises31 is limited regarding the magnitude of loading that is detrimental to the graft following ACL reconstruction.
A disadvantage with CKC exercises is that, due to their complex character, they may not isolate separate muscles sufficiently to achieve optimal increases in muscle strength. A weak quadriceps musculature will possibly not receive enough stimuli to regain maximal strength.140, 228 In contrast, OKC exercises isolate one muscle339 and demand considerably activity in the quadriceps musculature99 and are thereby essential for strength development.206 Still, there is no clear evidence that this type of exercise can be performed without risk.
Introduction
A few RCT studies have evaluated CKC and OKC exercises in ACL rehabilitation. Perry et al.250 reported no differences in laxity or knee function after rehabilitation in CKC or OKC in patients with ACL deficiency although data on muscle strength is not reported. Another study showed that patients with ACL reconstruction who trained with OKC exercises had greater anterior tibial translation compared to patients who trained with CKC exercises. However, there was a difference in translation only for the static knee stability (KT 1000) test with maximum applied force ‐ 1.6 mm in the CKC group vs. 3.3 mm in the OKC group. No information was obtained regarding muscle strength after the rehabilitation programs.46 In contrast, Mikkelsen et al.206 found that the addition of exercises in OKC after ACL reconstruction resulted in a significantly better improvement in quadriceps torque without reducing knee joint stability and led to a significantly higher number of athletes returning to their previous activity earlier and at the same level as before injury. Similarly, no differences in knee laxity in patients with ACL reconstruction who performed quadriceps exercises in CKC or OKC in the early period after surgery is reported.217 Moreover, there were no differences in functional improvement126 or knee pain214 between groups. Furthermore, CKC and OKC exercises have been compared in the middle period of rehabilitation after ACL reconstruction. There were no differences between groups regarding knee laxity or knee function.249 Heijne and Werner110 evaluated early versus late initiation of OKC exercises for quadriceps in patients with ACL reconstruction receiving either patellar tendon or hamstring tendon grafts. Early start of OKC exercises after ACL reconstruction with hamstring tendon graft resulted in increased knee laxity compared to late start and to both early and late start after ACL reconstruction with patellar tendon graft. On the contrary, in the patients receiving a patellar tendon graft the laxity did not differ between groups with early or late start of OKC exercises. This result is in line with other studies.37, 142, 289 Furthermore, early start of OKC exercises did not lead to increased quadriceps muscle torques in patients with hamstring tendon or with patellar tendon graft.110
Introduction
strength training, muscle volume is not increased proportional to the strength gains. Particularly in the early period of training a great proportion of the muscle strength can be attributed to neuronal adaptation resulting in enhanced motor unit activation.75, 138, 146, 251, 282
Application of appropriate load is central in strength training.2, 49, 76, 251, 252, 262, 336 Once muscles adapt to a stimuli, additional load needs to be placed on these structures to achieve further strength gains.251, 252, 262 Overload leads to compensatory hypertrophy and an increase in muscle strength.76, 138, 146 One repetition maximum (1RM) is defined as the heaviest resistance that can be lifted for one complete repetition of an exercise.76, 155 Load in exercise programs are generally expressed as percent of 1RM. The dose‐response relationship of strength development has shown to be different for untrained individuals, recreationally trained individuals, and athletes. Untrained individuals achieve maximal strength gains at a training intensity of about 60% of 1RM, recreationally trained individuals exhibit maximal strength gains with a mean intensity of 80% of 1RM, and athletes need a training intensity of 85% of 1RM to achieve optimal results.251, 252, 262
Total training volume in weight training is given by sets x repetitions x load accomplished.76 Performing three261, 271 or four262 sets per muscle group has been shown to be superior compared to one set for maximal strength gains in the leg muscles.
Training frequency is the number of exercise sessions per week. For maximized strength gains, two to three sessions per week has shown to be optimal.76 Effect size for frequency of training is reported to differ by training status. Untrained individuals elicited the greatest increases in strength with training of each muscle group three days per week, while trained individuals achieved optimal strength gains through training two days per week.262
Factors that may interfere with the rehabilitation
Musculoskeletal pain may affect the performance of exercises and alter the muscle activation pattern.122, 247, 311, 333 In addition, swelling in the knee joint may also contribute to a changed movement pattern. Since effusion has been shown to lead to quadriceps inhibition, it may interfere with quadriceps strengthening.78, 128, 153, 307 Therefore, most ACL rehabilitation programs incorporate early joint motion as it is beneficial for pain reduction and can
Introduction
minimize capsular contractions and normalize ROM. Goals in the early rehabilitation phase are full knee joint ROM, achieved muscular control, and reduced swelling.33, 35, 51, 193, 219, 266, 268, 269, 288, 289, 329
Furthermore, fear of pain affects the ability to move and the performance of the rehabilitation exercises. A patient can manage fear through confrontation or avoidance. Fear‐avoidance, which refers to avoidance of movements or activities based on fear, has been suggested to contribute to long term pain problems. Avoidance of movements and activities probably cause deterioration of the musculoskeletal system.177, 345 Pain related fear is associated with functional limitations in patients with osteoarthritis.116 Moreover, fear of re‐injury is common among patients with ACL reconstruction who do not succeed to return to their pre‐injury activity level.169 In addition, the psychological profile of the patients,96 and perceived self‐ efficacy (the judgment of oneʹs potential ability to carry out a task) 322 may be of importance for the rehabilitation outcome.
Assessment of knee joint function
Knee joint stability
In the clinical situation knee laxity is evaluated using a Lachman test59, 184, 232 and pivot shift test.59, 232, 233 A clinical examination provides a subjective grading of the knee motion. There is, however, poor agreement between clinical laxity test on an acute knee injury and magnetic resonance imaging (MRI) verified ACL rupture.90 In addition, there are great inter‐observer variations in the estimations.231 In research, analysis of knee joint motion have been made using in vitro approaches with cadavers,132, 180, 195, 281, 350 and in vivo methods including strain measurements,31 goniometer chains,164, 334
Introduction
tibial translation can be measured using CA‐4000,164, 334 KSS,263, 354 and Instrumented Spatial Linkage.194
Neuromuscular function
Muscle strength is commonly evaluated with isokinetic dynamometry after ACL injury or reconstruction. Low angular velocities (30 or 60°/sec)64, 65, 98, 118, 143, 150, 151, 211 and higher angular velocities (≥ 120°/sec)64, 65, 98, 118, 143, 150, 151, 199, 211, 338 have been used. In addition, assessment of 1RM or prediction of 1RM from submaximal tests is used to evaluate strength and to determine appropriate load when prescribing training.248 Moreover, a strength test battery, which includes knee extension, knee flexion, and leg press muscle power tests, can significantly reveal deficits in leg muscle power in patients with ACL deficiency or ACL reconstruction.224 Electromyography (EMG) analysis can assess muscle activation with respect to magnitude and timing. The EMG signal consists of the electrical signal of the neuromuscular activation.23
The most established test to measure proprioception is the threshold to detection of passive motion. Another frequently used test is the reproduction of passive positioning, which uses active reproduction of a previously positioned knee joint angle.89
Postural control is a person’s ability to control the body’s position in space while maintaining stability and orientation342 and can be assessed using measurements of balance in stance.3
Jump tests are frequently used to assess knee function in patients with ACL deficiency or reconstruction. Several jump tests and jump test batteries exist; a selection is described here. Vertical jump, hop for distance, drop jump followed by double hop for distance, square hop, and side hop have high test‐ retest reliability.108 A test battery including vertical jump, hop for distance and side hop is reported to have high ability to discriminate between the hop performance of the injured and uninjured leg in patients with ACL deficiency or ACL reconstruction.108 Noyes et al developed a series of one‐legged hop tests ‐ single, triple, cross‐over and timed hop tests ‐ to create a measure of alterations in lower limb function in patients with ACL deficiency.230 This
Introduction
series of hop test is reliable and valid for patients with an ACL reconstruction.258 These hop tests are included in a decision‐making scheme for classifying patients as rehabilitation versus surgical candidates based on their dynamic knee stability.81
Subjective knee function
The Lysholm score319 and the Knee Injury and Osteoarthritis Outcome Score (KOOS)272 are frequently used to evaluate subjective knee function in patients with ACL deficiency or reconstruction. The level of activity is regularly determined with the Tegner score.319 Knee related quality of life can be assessed using the ACL Quality of Life Questionnaire.168, 210 Moreover, pain related fear can be measured with the Tampa Scale for Kinesiophobia.169, 344 Self efficacy can be evaluated using the Knee Self‐Efficacy Scale, which is developed to evaluate prognostic and outcome expectations of perceived self‐ efficacy in patients with ACL deficiency.321
Rationale for the thesis
Anterior cruciate ligament injury is common among young active individuals, and many patients have remaining problems despite treatment. The rehabilitation aims to improve dynamic knee stability. The dynamic anterior tibial translation is of importance for the knee function. However, the effect of ACL reconstruction and/or rehabilitation on dynamic knee stability is not completely understood. Consequently, there is a need of more knowledge regarding the effect of different rehabilitation exercises and rehabilitation programs on knee joint motion and muscle activation in patients with ACL deficiency or ACL reconstruction. This information may imply that the rehabilitation can be adjusted to develop stability in the knee joint.
Aims
AIMS OF THE THESIS
General aim
The overall aim of this thesis was to study the dynamic knee stability during and after rehabilitation in individuals with ACL injury.Specific aims
1) To elaborate an evaluation method for muscle strength • To develop a systematic procedure for the establishment of one repetition maximum (1RM) (study II).• To investigate the intra‐ and inter‐rater reliability of 1RM of squat on one leg and seated knee extension on one leg (study II).
2) To evaluate the effect of exercises in closed and open kinetic chain
• To evaluate the effect of a specific exercise session on static and dynamic sagittal tibial translation in uninjured individuals (study I).
• To compare the effects of a comprehensive rehabilitation program supplemented with quadriceps strengthening in closed kinetic chain (CKC) with the same comprehensive rehabilitation program supplemented with quadriceps strengthening in open kinetic chain (OKC) in patients with acute ACL deficiency on static and dynamic sagittal tibial translation, muscle function, and subjective knee function (study III).
Aims
• To evaluate different rehabilitation exercises regarding dynamic anterior tibial translation and muscle activation five weeks after an ACL reconstruction (study IV).
3) To evaluate dynamic knee stability in patients with ACL deficiency or ACL reconstruction
• To compare anterior tibial translation and muscle activation during rehabilitation exercises in an ACL reconstructed knee with the same ACL injured knee before ACL reconstruction, and with the uninjured knee on the same patient (study IV).
Materials and methods
MATERIALS AND METHODS
Design
The thesis consists of the following studies:
• a methodological study performed on uninjured individuals, aiming to develop an evaluation method for muscle strength (study II).
• experimental laboratory studies to evaluate the effect of repeated knee exercises in uninjured individuals (study I) and to identify effective and safe knee exercises in patients with ACL reconstruction (study IV). • an experimental clinical study performed on patients with ACL
deficiency, to evaluate specific rehabilitation programs in a randomised study design (study III).
Overview of the studies
The thesis is mainly based on data collection of knee motion including tibial translation, registration of muscle activation, muscle strength and functional performance, and subjective ratings of knee function and activity level.
Study I
Sagittal tibial translation and muscle activation were measured on uninjured individuals before, during, and after a specific exercise session with heavy load, including cycling and maximum number of knee extensions and heel raises.
Study II
A systematic procedure for the establishment of 1RM was developed. The intra‐ and inter‐rater reliability of 1RM of a squat on one leg and seated knee
Materials and methods
extension on one leg was investigated on uninjured individuals using a test retest design.
Study III
Patients were tested (median 43 days, range 20‐96) after an ACL injury. Patients were randomised to a rehabilitation program supplemented with quadriceps strengthening in CKC or OKC. Aside from these exercises, the two rehabilitation programs were identical (paper III Appendix 1). Patients were assessed after four months of rehabilitation. Sagittal tibial translation, muscle strength, jump performance, muscle activation, and functional outcome were evaluated.
Study IV
Sagittal tibial translation and muscle activation were registered during rehabilitation exercises on patients before (uninjured and the ACL deficient knee) and five weeks after an ACL reconstruction (ACL reconstructed knee).
Subjects
Uninjured individuals and patients with an ACL deficiency or ACL reconstruction participated in the thesis (Table 1).
Materials and methods Table 1 Subjects included in the studies. Study Individuals Uninjured/ injured knee Number Age mean (range) Sex male/female I Uninjured 18 25 (20-33) 9/9 II Squat Uninjured 16 24 (20-27) 4/12 Knee extension Uninjured 27 25 (21-31) 16/11
III ACL def 42a 26 (15-44) 24/18 IV ACL rec 19 21 (16-31) 11/8 a49 patients were included in the RCT study; 20 of the patients in the CKC group (11 men and 9 women) and 22 patients in the OKC group (13 men and 9 women) completed the rehabilitation and follow‐up procedure. ACL def = ACL deficient knee, ACL rec = ACL reconstructed knee.
Study I and II
A convenient sample of uninjured volunteers aged 18 to 35 years was recruited.
Study III
Participants were recruited consecutively from patients attending the orthopaedic department after knee trauma from December 2002 to January 2006. Patients were informed about the study and were asked to participate if they were 15 to 45 years old and had a unilateral ACL rupture that was no more than 14 weeks old. Patients were excluded if they had additional injury or previous surgery to the lower extremities, with the exception of partial meniscal injury or minor collateral ligament injury in the injured knee joint or partial meniscectomy in the injured or contralateral knee. All ACL injuries were verified by arthroscopy or MRI. Forty‐nine patients were randomly assigned to one of the two treatment groups using a concealed allocation procedure, and 42 patients fulfilled the rehabilitation program and the
Materials and methods
assessments. Numbers of isolated and combined ACL injures were not significantly different between groups.
Study IV
Participants were recruited consecutively from patients who were diagnosed with unilateral ACL rupture and were on the waiting list for ACL reconstruction with a quadruple hamstring tendon graft from October 2004 to May 2006. Patients were informed about the study and were asked to participate if they were 15 to 45 years old and had a unilateral ACL rupture that was no more than 4 years old. Exclusion criteria were other total ligament rupture, menisci suture in the injured knee joint, total ligament rupture, or reconstruction on the contralateral knee. All patients followed a carefully defined rehabilitation program (paper IV). Immediately after being operated on, the patients were allowed unrestricted range of motion exercises plus quadriceps sets and straight leg raise. Weight‐bearing when walking was allowed after one week, and single crutch weight bearing indoors after two weeks.
Equipment
Electrogoniometer
A computerised goniometer linkage, CA‐4000 (OSI Inc., Hayward CA, USA), was used to measure the flexion angle and sagittal tibial translation (Figure 2). The system is composed of three parts: the femoral and tibial frames, and a rotation module. Three potentiometers in the rotation module measure the relative rotations between the femur and tibia. The potentiometer for sagittal
Materials and methods Figure 2 The CA‐4000 system mounted on a subject. a = potentiometer registering knee extension ‐ flexion, b = potentiometer registering sagittal plane motion. The CA‐4000 was zeroed at the beginning of each assessment with the subject lying supine on the examination table and the knee relaxed to full extension. This position is a neutral reference that is used to define tibial position during motion. A passive knee extension was performed to identify a reference position at each flexion angle for the calculation of dynamic translation. The passive extension was done from >100° knee flexion to hyperextension. The subject was sitting on the examination table with back support, with approximately 70° hip flexion. The passive extension was repeated two to four times during the test procedure to control calibration. Data were sampled from the potentiometers by a computer at a rate of 2000 Hz.
The mechanical accuracy of the CA‐4000 electrogoniometer is ± 0.7 mm within the normally used sagittal measurement range.334 The CA‐4000 also has satisfactory validity throughout a range of motion when compared to fluoroscopy. The CA‐4000 was validated during stair ascent in 10 patients with ACL deficiency and 10 controls. The correlations between the electrogoniometric and fluoroscopic measurements were r > 0.89 when patella
a a
b
